20 Overview of the Guile API

Guile's application programming interface (API) makes
functionality available that an application developer can use in either
C or Scheme programming. The interface consists of elements that
may be macros, functions or variables in C, and procedures, variables,
syntax or other types of object in Scheme. Broadly speaking, the
interface as a whole can be divided into three groups.

Elements that are available equivalently as C functions or Scheme
procedures.

Elements that are only available as macros, functions or variables for C
programming.

Elements that are only available as procedures or other objects in
Scheme.

Functions/procedures in the first group are often known as
primitives, subrs or builtins. An example is the
assq Scheme procedure, which is also available as scm_assq
in C.

Elements in the second and third groups exist because they provide
additional language-specific benefits in either Scheme or C. Examples
are the C macro SCM_CONSP, which is faster and more convenient in
C programming than the primitive scm_pair_p, and the
procedure-with-setter make-object-property, which provides a
more convenient property handling interface in Scheme than the
primitives on which it is based.